A sprung balance resonator generally has a configuration like that shown in FIG. 2. Thus, the resonator 1 includes a balance 3 driven onto a staff 7 so that it is rotatably mounted between a bridge and the bottom plate of a timepiece movement.
As shown in FIG. 2, in order to transmit its oscillation frequency to the escape system, balance 3 includes a pin 6 fitted in a recess of said balance. The balance spring 5 is fitted on the other side of the shoulder 8 of staff 7. The balance spring 5 includes a hairspring 2 formed in single piece with a collet 4, which is fitted onto staff 7.